The present invention relates generally to an adaptive equalizer for variable length sound tubes utilizing an acoustical time of flight measurement.
Some users of earpiece accessories have a strong preference for certain types of sound delivery systems over others (e.g., an accessory sound delivery tube that terminates in the ear canal versus an intraconcha (inside the bowl of the ear) device). The equalization used to control acoustical standing waves in the earpiece tubing has been shown to have a key role in lowering the threshold of feedback in the earpiece as well as improving the quality of the audio presented to the user. The standing wave frequencies are a function of the combined length of the sound tube and accessory tube; and therefore, the equalization must be tuned to the particular delivery system used. For example, an accessory that terminates near the entrance to the ear canal results in a total tube length different than one that is inserted into the ear canal. This requires a realignment of the equalization in order to maintain feedback suppression and optimum sound quality.
Thus, there exists a need for being able to recognize the length of the accessory sound tube that is connected to the earpiece in order to select the proper settings for the equalizer.